Short-distance contactless communication apparatus and method thereof

ABSTRACT

A short-distance contactless communication apparatus includes: a receiver configured to operate under at least a first receiving mode and a second receiving mode, wherein the receiver receives a modulation signal with a first modulation scheme when the receiver is configured to operate under the first receiving mode, and the receiver receives a modulation signal with a second modulation scheme when the receiver is configured to operate under the second receiving mode, and wherein the receiver utilizes an oscillation signal to receive the modulation signal, and the oscillation signal utilized by the receiver is derived from the modulation signal or derived from a reference clock of a local source based on the receiving mode of the receiver.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/873,442, which was filed on 2013 Sep. 4 and is included herein by reference.

BACKGROUND

The present invention relates to a short-distance contactless communication apparatus and method thereof, and more particularly to a short-distance contactless communication apparatus capable of adjusting the envelope of a receiving modulation signal, and method thereof.

Short-range, standards-based contactless connectivity technology such as Near field communication (NFC) uses magnetic field induction to enable communication between electronic devices inclose proximity. Based on RFID technology, NFC provides a medium for the identification protocols that validates secure data transfer. Conventionally, a NFC device encompasses a PCD (Proximity Coupling Device) transceiver and a PICC (Proximity Inductively Coupled Card) receiver. When the NFC device is configured as an initiator (i.e. the PCD mode), the transmitter in the PCD transceiver is used to emit a modulation signal to another NFC device, i.e. the target NFC device. Meanwhile, the receiver in the PCD transceiver receives the emitted modulation signal as an in-band blocking signal or an in-band blocker. Upon detecting the modulation signal transmitted from the transmitter of the PCD transceiver, the target NFC device responds with a load modulation (LM) signal to the receiver of the PCD transceiver. On the other hand, when the NFC device is configured as a PICC target (i.e. the PICC mode), the PICC receiver receives a modulation signal transmitted from another PCD device (i.e. the initiator). Therefore, no matter the NFC device is configured as PCD mode or PICC mode, the NFC device always needs to receive a modulation signal. However, the voltage swing or the power of the modulation signal is depended on the relative position between the two NFC devices, and the matching network and the antenna coils of the two NFC devices. If the voltage swing or the power of the modulation signal is too large, it may exceed the dynamic range of the receiver of the NFC device. If the voltage swing or the power of the modulation signal is too small, the modulation signal may not be accurately demodulated by the NFC device. Therefore, providing an NFC device capable of accurately receiving the modulation signal during the PCD mode and the PICC mode is an urgent problem in the NFC field.

SUMMARY

One of the objectives of the present invention is to provide a short-distance contactless communication apparatus capable of adjusting the envelope of a receiving modulation signal, and method thereof.

According to a first embodiment of the present invention, a short-distance contactless communication apparatus is disclosed. The short-distance contactless communication apparatus comprises a receiver configured to operate under at least a first receiving mode and a second receiving mode, wherein the receiver receives a modulation signal with a first modulation scheme when the receiver is configured to operate under the first receiving mode, and the receiver receives a modulation signal with a second modulation scheme when the receiver is configured to operate under the second receiving mode. The receiver utilizes an oscillation signal to receive the modulation signal, and the oscillation signal utilized by the receiver is derived from the modulation signal or derived from a reference clock of a local source based on the receiving mode of the receiver.

According to a second embodiment of the present invention, a short-distance contactless communication apparatus is disclosed. The short-distance contactless communication apparatus comprises a receiver capable of operating under a proximity coupling mode and/or a proximity inductively coupled card mode and an adjusting device. The receiver is coupled to a signal receiving port of the short-distance contactless communication apparatus. The adjusting device is coupled to the signal receiving port for adjusting a peak voltage level of a modulation signal on the signal receiving port to fall within a predetermined voltage range.

According to a third embodiment of the present invention, a short-distance contactless communication method is disclosed. The short-distance contactless communication method comprises the steps of: using a receiver capable of operating under a proximity coupling device (PCD) mode and/or a proximity inductively coupled card (PICC) mode to couple to a signal receiving port; and adjusting a peak voltage level of a modulation signal on the signal receiving port to fall within a predetermined voltage range.

According to a fourth embodiment of the present invention, a NFC device comprising an NFC integrated circuit (IC) capable of supporting PCD and PICC reception is disclosed. The NFC device comprises PCD and PICC receivers have a common input port, a fixed resistor coupled to the common input port, an envelope detector coupled to the common input port, a programmable resistor circuit having a first node coupled to the common input port and a second node coupled to ground. The resistance of the programmable resistor circuit is adjusted according to the peak voltage level at the input of the envelope detector, and the adjustment of the programmable resistor circuit continues until the peak voltage at the input of the envelope detector is within a predetermined voltage range.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a short-distance contactless communication apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a short-distance contactless communication apparatus operated under a first mode according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a short-distance contactless communication apparatus operated under a second mode according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating the voltage level of a modulation signal on a signal receiving port before and after the adjustment of an adjusting device according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating a predetermined voltage range that is considered to be the optimum to a peak voltage level of a modulation signal according to an embodiment of the present invention.

FIG. 6 is a diagram illustrating an embodiment of a programmable resistor according to an embodiment of the present invention.

FIG. 7 is a diagram illustrating an embodiment of an envelope detector according to an embodiment of the present invention.

FIG. 8 is a diagram illustrating a PICC receiver according to an embodiment of the present invention.

FIG. 9 is a diagram illustrating a PCD receiver according to an embodiment of the present invention.

FIG. 10 is a diagram illustrating a short-distance contactless communication integrated circuit according to another embodiment of the present invention.

FIG. 11 is a diagram illustrating a receiver according to an embodiment of the present invention.

FIG. 12 is a flowchart illustrating a short-distance contactless communication method according to an embodiment of the present invention.

DETAILED DESCRIPTION

Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, electronic equipment manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.

Please refer to FIG. 1, which is a diagram illustrating a short-distance contactless communication apparatus (e.g. a near-field communication (NFC) apparatus 100) according to an embodiment of the present invention. It is noted that NFC is just an example of the short-distance contactless communication, and this is not a limitation of the present invention. The NFC apparatus 100 comprises an NFC integrated circuit 102, an EMI (Electromagnetic interference) low-pass filter 104, a matching network 106, a phase shifting network 108, and an antenna 110. The NFC integrated circuit 102 is arranged to transmit a NFC signal and/or to receive a NFC signal. The NFC integrated circuit 102 comprises a baseband processor 1022, a first mode receiver, such as a proximity coupling device (PCD) receiver 1024, a second mode receiver, such as a proximity inductively coupled card (PICC) receiver 1026, an adjusting device 1028, a first mode transmitter, such as a PCD transmitter 1030, and a switching circuit 1032. The NFC integrated circuit 102 in this embodiment has at least five signal ports (i.e. IC pad) ANTP, RX, TXP TXN, ANTN. The signal ports ANTP and ANTN are differential ports coupled to the switching circuit 1032. The signal transmitting ports TXP and TXN are differential ports coupled to the PCD transmitter 1030. The signal receiving port RX is the common port coupled to the PCD receiver 1024, the PICC receiver 1026, and the adjusting circuit 1028. On the other side, the matching network 106 is coupled to the signal ports ANTP and ANTN. The EMI low-pass filter 104 is coupled to the signal transmitting ports TXP and TXN. The phase shifting network 108 is coupled to the signal receiving port RX. Note that the configuration of the signal ports is for illustrative purpose rather than limitations for the present invention. In other embodiment, the antenna port and the transmitting ports can be single-ended, the receiving port can be differential, and the phase shifting network 108 can be duplicated to provide inputs to the differential receiving ports.

In this embodiment, the NFC integrated circuit 102 is a single-chip. The EMI low-pass filter 104, the matching network 106, the phase shifting network 108, and the antenna 110 are external to the NFC integrated circuit 102.

The EMI low-pass filter 104 comprises a first inductor 104 a, a second inductor 104 b, a first capacitor 104 c, and a second capacitor 104 d. The matching network 106 comprises a first capacitor 106 a, a second capacitor 106 b, a third capacitor 106 c, a fourth capacitor 106 d, a fifth capacitor 106 e, and a sixth capacitor 106 f. The phase shifting network 108 comprises a resistor R130 and a capacitor C130. The connectivity of the above circuit elements is shown in FIG. 1, and the detailed description is omitted here for brevity. However, the connectivity shown in FIG. 1 is for illustrative purpose, rather than a limitation of the present invention. In FIG. 1, the resistor R130 connects to the capacitor C130 in series, and the resistor and the capacitor C130 are connected between the signal receiving port RX and the terminal N1.

More specifically, the EMI low-pass filter 104 is arranged to filter out the EMI signal of the transmitting NFC signal generated by the PCD transmitter 1030. The matching network 106 is arranged to perform impedance matching between the antenna 110 and the EMI low-pass filter 104 and the impedance matching between the antenna 110 and the switching circuit 1032. The phase shifting network 108 provides a path to receive the NFC signal from the antenna 110 to the PCD receiver 1024 and the PICC receiver 1026 or to receive the transmitting NFC signal from the EMI low-pass filter 104 to the PCD receiver 1024.

In the NFC integrated circuit 102, the baseband processor 1022 is coupled to the PCD receiver 1024, the PICC receiver 1026, the adjusting device 1028, the PCD transmitter 1030, and the switching circuit 1032. The switching circuit 1032 comprises a first switch 1032 a and a second switch 1032 b. The adjusting device 1028 is arranged for presently adjusting a peak voltage level of a modulation signal Sm on the signal receiving port RX to fall within a predetermined voltage range when the modulation signal Sm appears on the signal receiving port RX. In other words, the adjusting device 1028 adjusts the modulation signal Sm in real time. The adjusting device 1028 comprises a programmable impedance component, such as a programmable resistor 1028 a, and an envelope detector 1028 b. The programmable resistor 1028 a has a first terminal coupled to the signal receiving port RX and a second terminal coupled to a reference voltage, e.g. the ground voltage Vgnd, for providing impedance between the signal receiving port RX and the ground voltage Vgnd according to an adjusting signal Sad. The envelope detector 1028 b is coupled to the signal receiving port RX and the baseband processor 1022 for detecting an envelope of the modulation signal Sm to generate a detecting signal Sd. The baseband processor 1022 receives the detecting signal Sd and accordingly generates the adjusting signal Sad to adjust the impedance of the programmable resistor 1028 a such that the peak voltage level of the modulation signal Sm on the signal receiving port RX falls within the predetermined voltage range.

It should be noted that the adjusting device 1028 is not limited to adjust the peak voltage level of the modulation signal Sm on the signal receiving port RX to fall within the predetermined voltage range, the adjusting device 1028 may be arranged to adjust the peak voltage level of the modulation signal Sm on the signal receiving port RX to be a predetermined voltage level or to adjust the peak voltage level of the modulation signal Sm on the signal receiving port RX to be a predetermined voltage level in the predetermined voltage range.

According to the embodiment, the NFC apparatus 100 (or the NFC integrated circuit 102) can be configured to operate under a PCD mode or a PICC mode. During the PCD mode, the NFC apparatus 100 functions as an initiator, i.e. the reader. During the PICC mode, the NFC apparatus 100 functions as a card.

When the NFC apparatus 100 is configured as the initiator during the PCD mode, the differential PCD transmitter 1030 emits an ASK modulation signal to the antenna 110 through the EMI low-pass filter 104, which is an optional device, and the matching network 106. The first switch 1032 a and the second switch 1032 b are closed to connect the capacitor 106 c and 106 e to the ground voltage Vgnd respectively. Before the PCD receiver 1024 receives a load modulation (LM) signal from the target NFC apparatus (not shown), which is configured as a card (i.e. PICC mode), the NFC apparatus 100 is re-configured. When the NFC apparatus 100 is re-configured, the PCD transmitter 1030 emits a transmitting modulation signal St to the target NFC apparatus. The transmitting modulation signal St is a continuous wave (CW) signal having an oscillating frequency substantially equal to 13.56 MHz as shown in FIG. 2. FIG. 2 is a diagram illustrating the NFC apparatus 100 operated under the PCD mode according to an embodiment of the present invention. As the phase shifting network 108 is directly connected to the EMI low-pass filter 104 via the terminal N1, the large transmitting modulation signal St will appear at the input (i.e. the signal receiving port RX) of the PCD receiver 1024 as an in-band blocker. Upon detecting the transmitting modulation signal St from the NFC apparatus 100, the target NFC apparatus will respond with a load modulation (LM) signal to the NFC apparatus 100. The LM signal will pass through the matching network 106 and the phase shifting network 108 before it is demodulated and decoded by the to the PCD receiver 1024.

On the other hand, when the NFC apparatus 100 is configured as the card during the PICC mode, the NFC apparatus 100 receives a receiving modulation signal Sr from the other NFC apparatus which is configured as an initiator. The receiving modulation signal Sr is an ASK modulation signal. The receiving modulation signal Sr is received through the antenna 110, the matching network 106, and the phase shifting network 108 before it is demodulated and decoded by the PICC receiver 1026 as shown FIG. 3. FIG. 3 is a diagram illustrating the NFC apparatus 100 operated under the PICC mode according to an embodiment of the present invention. When the NFC apparatus 100 is configured as the PICC mode, the PICC receiver 1026 responds to the PCD transmitter (i.e. the other NFC apparatus) by modulating the antenna load, which is known as load modulation, using the first switch 1032 a and the second switch 1032 b. It is noted that there are many ways to modulate the antenna load without change the essence of the present invention.

Accordingly, no matter the NFC apparatus 100 is configured to operate under the PCD mode or the PICC mode, the voltage level of the modulation signal Sm on the signal receiving port RX should be fall within an appropriate range such that the PCD receiver 1024 or the PICC receiver 1026 can receive the modulation signal Sm (e.g. the load modulation signal or the receiving modulation signal Sr) correctly.

According to the embodiment, the fixed resistor R130 in the phase shifting network 108 forms a voltage divider with the input impedance ZRX at the signal receiving port RX of the NFC integrated circuit 102. After the values of the resistor R130 and the capacitor C130 are determined, the voltage level of the modulation signal Sm on the signal receiving port RX may only be adjusted by the programmable resistor 1028 a in the adjusting device 1028 such that the voltage level of the modulation signal Sm on the signal receiving port RX is adjusted into the usable input dynamic range of the PCD receiver 1024 or the PICC receiver 1026. Please refer to FIG. 4, which is a diagram illustrating the voltage level of the modulation signal Sm on the signal receiving port RX before and after the adjustment of the adjusting device 1028 according to an embodiment of the present invention. FIG. 4 also shows the corresponding programmable resistor 1028 a and the resistor R130 in the form of circuit divider.

In the left side of FIG. 4, the impedance of the programmable resistor 1028 a is set to the default maximum value Rmax before the adjustment of the adjusting device 1028. The threshold voltage level corresponding to the maximum dynamic range of the PCD receiver 1024 (or the PICC receiver 1026) is VTH0. When the modulation signal Sm appears on the common terminal VB (i.e. the signal receiving port RX) during the PCD mode or the PICC mode, the envelope detector 1028 b starts to detect the envelope of the modulation signal Sm. When the baseband processor 1022 determines that the peak voltage value of the modulation signal Sm on the common terminal VB is V1, which is larger than the predetermined threshold voltage level VTH0, this means that the voltage level of the modulation signal Sm is larger than the dynamic range of the NFC integrated circuit 102, and this may saturate the PCD receiver 1024 (or the PICC receiver 1026). Then, the baseband processor 1022 starts to adjust (e.g. decrease) the resistance of the programmable resistor 1028 a by using the adjusting signal Sad until the peak voltage level of the modulation signal Sm reaches the voltage level VTH0 as shown in the right side of FIG. 4. Accordingly, the envelope of the modulation signal Sm falls within the dynamic range of NFC integrated circuit 102 when the resistance of the programmable resistor 1028 a is reduced to Ra from the maximum value Rmax.

In addition, the resistance of the programmable resistor 1028 a is set to be the maximum value as default, and is gradually reduced by the adjusting device 1028 in real time. This ensures that the envelope of the modulation signal Sm on the common terminal VB always has the maximized carrier-to-noise (CNR) ratio after the adjustment of the adjusting device 1028. Nevertheless, other methods of adjusting the resistor R130 are also possible. Moreover, the resistor R130 is placed externally in this embodiment, and this will provide the flexibility of one-time adjustment with respect to different antenna designs. Obviously, the resistor R130 can also be integrated into the NFC integrated circuit 102.

According to the present method, when the signal level of the receiving signal (i.e. the modulation signal Sm) is too high and beyond the receiver dynamic range, the adjusting device 1028 reduces the resistance of the programmable resistor 1028 a to make the signal level of the receiving signal to fall within the dynamic range. When the signal level of the receiving signal is too small and fails to be detected by the PCD receiver 1024 (or the PICC receiver 1026), the adjusting device 1028 increases the resistance of the programmable resistor 1028 a to increase the signal level of the receiving signal.

It is noted that the adjusting device is not limited to adjust the peak voltage level of the modulation signal Sm to equal a predetermined voltage level, the adjusting device 1028 may also be designed to adjust the peak voltage level of the modulation signal Sm to fall within a predetermined voltage range as long as the envelope of the modulation signal Sm falls within the dynamic range of NFC integrated circuit 102, which also belongs the scope of the present invention. FIG. 5 is a diagram illustrating a predetermined voltage range that is considered to be the optimum to the peak voltage level of the modulation signal Sm according to an embodiment of the present invention. The predetermined voltage range varies from a minimum threshold voltage VTHmin to a maximum threshold voltage VTHmax. In other words, the above embodiment having a fixed target voltage level is a special case of this embodiment where the minimum threshold voltage VTHmin is the same as the maximum threshold voltage VTHmax.

According to the embodiment, the adjustment of the adjusting device 1028 will stop when the peak voltage level of the envelope of the modulation signal Sm at the common terminal VB falls within the dynamic voltage range of the NFC integrated circuit 102. If the peak voltage level of the envelope of the modulation signal Sm is still below the minimum threshold voltage VTHmin while the resistance of the programmable resistor 1028 a is already in the maximum resistance, then the adjusting device 1028 will terminate the adjustment. Similarly, if the peak voltage level of the envelope of the modulation signal Sm still exceeds the maximum threshold voltage VTHmin while the resistance of the programmable resistor 1028 a is already in the minimum resistance, then the adjusting device 1028 will also terminate the adjustment.

By using the present adjusting device 1028, the value of the resistor R130 needs not to be very accurately determined during the design phase because the programmable resistor 1028 a will automatically compensate the measurement error or the component variation of the resistor R130 during the PCD mode or the PICC mode. In fact, if the dynamic range of the programmable resistor 1028 a is sufficiently large, the adjustment of the resistor R130 during the design phase can be eliminated, thus allowing the resistor R130 to be integrated into the NFC integrated circuit 102.

Please refer to FIG. 6, which is a diagram illustrating an embodiment of the programmable resistor 1028 a according to an embodiment of the present invention. The programmable resistor 1028 a comprises a plurality of switches S1-SN and a plurality of resistors R1-RN. One switch is connected to a corresponding resistor in series. The adjusting signal Sad is a digital signal, and is arranged to selectively control the on/off of the plurality of switches S1-SN to control the effective resistance between the common terminal VB and the ground. It is noted that there are many embodiments to realize the programmable resistor 1028 a without changing the essence of the present method.

Please refer to FIG. 7, which is a diagram illustrating an embodiment of the envelope detector 1028 b according to an embodiment of the present invention. The envelope detector 1028 b comprises an operational amplifier AMP, a P-type field-effect transistor (PMOS) M1, a capacitor C1, and an analog-to-digital converter ADC. The negative terminal (−) of the operational amplifier AMP is coupled to the common terminal VB for receiving the modulation signal Sm. When the envelope of the modulation signal Sm falls below a predetermined threshold Vp, the P-type field-effect transistor M1 is turned on to charge the capacitor C1 by voltage Vg. The voltage across the capacitor C1 will continue to increase until the voltage Vp equals the envelope of the modulation signal Sm. Then, the P-type field-effect transistor M1 is turned off by voltage Vg. This mechanism allows the circuit to track the envelope of the modulation signal Sm. The analog-to-digital converter ADC is used to feedback the voltage Vp to the baseband processor 1022 for determining the peak voltage level of the envelope of the modulation signal Sm.

It is noted that, in another embodiment of the present invention, when the NFC apparatus 100 is configured to be the PCD mode, the adjustment scheme is activated only when NFC apparatus 100 is transmitting a continuous wave signal. When the NFC apparatus 100 is configured to be the PICC mode, the adjustment scheme is activated to detect the magnetic field (i.e. the receiving modulation signal Sr) from the other PCD.

In another embodiment of the present invention, the adjustment scheme is activated periodically when the PCD transmitter 1030 is transmitting the modulation signal St. In this embodiment, the adjustment scheme is always activated during the PICC mode.

Please refer to FIG. 8, which is a diagram illustrating the PICC receiver 1026 according to an embodiment of the present invention. The PICC receiver 1026 comprises a comparator 1026 a, a diode 1026 b, a first resistor 1026 c, a second resistor 1026 d, and a capacitor 1026 e. The first resistor 1026 c is coupled between the negative input terminal (−) of the comparator 1026 a, and the negative input terminal (−) of the comparator 1026 a is coupled to the common terminal VB (i.e. the signal receiving port RX) of the NFC apparatus 100. The positive input terminal (+) of the comparator 1026 a is coupled to a reference DC voltage Vdc. The anode of the diode 1026 b is coupled to the output of the comparator 1026 a and the cathode of the diode 1026 b is coupled to a low pass filer, in which the low-pass filter is comprised of the second resistor 1026 d and the capacitor 1026 e. The element connectivity of the PICC receiver 1026 has been shown in FIG. 8, thus the detailed description is omitted here for brevity. For illustrative purposes, the resistor R130 and the capacitor C130 are also shown in FIG. 8. The ASK modulation signal is inputted to the capacitor C130. The incoming ASK modulation signal has two distinct amplitude levels, i.e. V1 (indicating no ASK modulation) and V2 (indicating some level of ASK modulation). When the voltage V1 is higher than the reference DC voltage Vdc, the capacitor 1026 e is charged, and the voltage level at node V0 increases. When the reference DC voltage Vdc is higher than the voltage V2, the capacitor 1026 e is discharged through the second resistor 1026 d and the voltage level at the node V0 decreases. The resulting waveform at the node V0 is the demodulated ASK signal as shown in FIG. 8.

Please refer to FIG. 9, which is a diagram illustrating the PCD receiver 1024 according to an embodiment of the present invention. The PCD receiver 1024 comprises a first mixer 1024 a, a first high-pass filter 1024 b, a first programmable-gain amplifier 1024 c, a first low-pass filter 1024 d, a first ADC 1024 e, a second mixer 1024 f, a second high-pass filter 1024 g, a second programmable-gain amplifier 1024 h, a second low-pass filter 1024 i, a second ADC 1024 j, a baseband processor 1024 k, an oscillator 10241, and a phase shifter 1024 m. The first mixer 1024 a and the second mixer 1024 f are coupled to the common terminal VB (i.e. the signal receiving port RX) of the NFC apparatus 100. The phase shifter 1024 m is arranged to provide two oscillation signals having 90° phase difference, one is provided to the first mixer 1024 a, and the other is provided to the second mixer 1024 f. The gains of the first programmable-gain amplifier 1024 c and the second programmable-gain amplifier 1024 h are controlled by the baseband processor 1024 k. The element connectivity of the PCD receiver 1024 has been shown in FIG. 9, thus the detailed description is omitted here for brevity. The load modulation signal is inputted to the terminal VB. The PCD receiver 1024 is a quadrature down-conversion receiver. Therefore, the demodulation of the amplitude and phase information of the load modulation signal can be realized by the PCD receiver 1024. Direct conversion receiver (DCR) with a band-pass filter is used for PCD receiver as it rejects the large transmitter leakage from the PCD transmitter meanwhile retains the load modulation signal at the subcarrier frequency as shown in FIG. 9. In the PCD mode, an automatic gain control (AGC) scheme can be used to adjust the gains of the first programmable-gain amplifier 1024 c and the second programmable-gain amplifier 1024 h according to the levels of the sub-carriers, thus helping to maintain a relatively constant sub-carrier level at the ADC input. It is noted that the most important circuits in the PCD receiver 1024 are the direct conversion mixer (i.e. 1024 a and 1024 f) and the high-pass filter (i.e. 1024 b and 1024 g). The addition of any circuits before the mixer, the removal of the low-pass filter (i.e. 1024 d and 1024 i), or moving the low-pass filter to place before the high-pass filter will not change the benefits of the PCD receiver 1024.

Moreover, the proposed adjustment scheme can be implemented for all types of PCD and PICC receivers with different demodulator architectures. The separate PCD and PICC receivers 1024, 1026 can also be merged into a single receiver without affecting the operation of the proposed adjustment scheme as shown in FIG. 10. In other words, the single receiver may comprise the functions of the PCD and PICC receivers 1024, 1026, which also belongs to the scope of the present invention.

In another embodiment, the proposed adjustment scheme can also be implemented in a NFC integrated circuit 102 having the PCD receiver 1024 and the PCD transmitter 1030, i.e. without the PICC receiver 1026.

FIG. 10 is a diagram illustrating the NFC integrated circuit 1002 according to another embodiment of the present invention. For illustrative purpose, the EMI low-pass filter 104, the matching network 106, the phase shifting network 108, and the antenna 110 are also shown in FIG. 10. The NFC integrated circuit 1002 comprises a baseband processor 10022, a receiver 10026, an adjusting device 10028, a PCD transmitter 10030, and a switching circuit 10032. It is noted that the baseband processor 10022, the adjusting device 10028, the PCD transmitter 10030, and the switching circuit 10032 are similar to the baseband processor 1022, the adjusting device 1028, the PCD transmitter 1030, and the switching circuit 1032 respectively, thus the detailed description is omitted. In this embodiment, the receiver 10026 is a combined circuit that comprises the functions of the PCD and PICC receivers 1024, 1026.

Please refer to FIG. 11, which is a diagram illustrating the receiver 10026 according to an embodiment of the present invention. The receiver 10026 comprises a first mixer 10026 a, a first low-pass filter 10026 b, a first programmable-gain amplifier 10026 c, a first high-pass filter 10026 d, a first ADC 10026 e, a second mixer 10026 f, a second low-pass filter 10026 g, a second programmable-gain amplifier 10026 h, a second high-pass filter 10026 i, a second ADC 10026 j, a limiter 10026 k, a phase-locked loop 10026 l, a multiplexer 10026 m, and a phase shifter 10026 n. The receiver 10026 is a single direct conversion receiver for both the PCD and PICC operation. The first mixer 10026 a and the second mixer 10026 f are coupled to the common terminal VB (i.e. the signal receiving port RX) of the NFC apparatus 100. The modulation signal is inputted to the terminal VB. The multiplexer 10026 m is controlled by the operation mode of the receiver 10026. When the receiver 10026 operates under the PICC mode, the multiplexer 10026 m passes the output of the limiter 10026 k to the phase shifter 10026 n. When the receiver 10026 operates under the PCD mode, the multiplexer 10026 m passes the output of the phase-locked loop 10026 l to the phase shifter 10026 n. The phase shifter 10026 n is arranged to provide two oscillation signals having 90° phase difference, one is provided to the first mixer 10026 a, and the other is provided to the second mixer 10026 f. The phase-locked loop 10026 l can be an integer-N PLL, or a fractional-N PLL. A control signal will be triggered so that the multiplexer 10026 m will select its input from the phase-locked loop 10026 l. The element connectivity of the receiver 10026 has been shown in FIG. 11, thus the detailed description is omitted here for brevity.

More specifically, when the receiver 10026 operates under the PICC mode, the limiter 10026 k is arranged to use the modulation signal at the terminal VB to generate the oscillation signal with 13.56 MHz, but not a limitation, to the phase shifter 10026 n. More specifically, in the PICC mode, the oscillation signal is obtained from the carrier of the incoming ASK signal at the terminal VB. This can be done by simply passing the ASK signal through an amplitude limiter (i.e. the limiter 10026 k). In the PICC mode, the control signal of the multiplexer 10026 m is toggled so that the multiplexer 10026 m obtains its input from the output of the limiter 10026 k.

When the receiver 10026 operates under the PCD mode, the phase-locked loop 10026 l is arranged to use the external reference clock of a local source to generate the oscillation signal with 13.56 MHz, but not a limitation, to the phase shifter 10026 n. The oscillation signals generated by the phase shifter 10026 n are provided to the ADCs 10026 e and 10026 j.

In summary, the operation of the proposed adjustment scheme in FIG. 1 (or FIG. 10) can be summarized into the following steps in FIG. 12. FIG. 12 is a flowchart illustrating an NFC method 1200 according to an embodiment of the present invention. Provided that substantially the same result is achieved, the steps of the flowchart shown in FIG. 12 need not be in the exact order shown and need not be contiguous; that is, other steps can be intermediate. The power amplifying method 1200 comprises the steps:

Step 1202: Use the PCD receiver 1024 to couple to the signal receiving port RX;

Step 1204: Use the PICC receiver 1026 to couple to the signal receiving port RX;

Step 1206: Use the programmable resistor 1028 a to provide an impedance between the signal receiving port RX and the ground voltage Vgnd according to an adjusting signal Sad;

Step 1208: Detect the envelope of the modulation signal Sm to generate the detecting signal Sd; and

Step 1210: Receive the detecting signal Sd and accordingly generate the adjusting signal Sad to adjust the impedance of the programmable resistor 1028 a such that the peak voltage level of the modulation signal Sm on the signal receiving port RX falls within the predetermined voltage range.

Briefly, the present invention is to instantly detect the peak voltage level of the modulation signal Sm on the signal receiving port RX of the NFC integrated circuit 102, and accordingly adjust the peak voltage level of the modulation signal Sm to fall within the dynamic range of the NFC integrated circuit 102 by adjusting the programmable resistor 1028 a. The adjustment scheme can be activated when transmitting a continuous wave signal, and/or in the PCD mode and/or the PICC mode. By using the proposed adjustment scheme, the value of the resistor R130 needs not to be very accurate during the design phase because the programmable resistor 1028 a can be used to adjust the peak voltage level of the modulation signal Sm to fall within the dynamic range of the NFC integrated circuit 102, and the resistor R130 can also be integrated into the NFC integrated circuit 102.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

What is claimed is:
 1. A short-distance contactless communication apparatus, comprising: a receiver, configured to operate under at least a first receiving mode and a second receiving mode, wherein the receiver receives a modulation signal with a first modulation scheme when the receiver is configured to operate under the first receiving mode, and the receiver receives a modulation signal with a second modulation scheme when the receiver is configured to operate under the second receiving mode; wherein the receiver utilizes an oscillation signal to receive the modulation signal, and the oscillation signal utilized by the receiver is derived from the modulation signal or derived from a reference clock based on the receiving mode of the receiver.
 2. The short-distance contactless communication apparatus of claim 1, wherein the receiver comprises: a mixer, arranged for receiving the modulation signal and the oscillation signal; and a high-pass filter, arranged to couple to an output of the mixer.
 3. The short-distance contactless communication apparatus of claim 1, wherein the receiver comprises: a limiter, arranged for receiving the modulation signal; a phase-locked loop, arranged for receiving the reference clock; and a multiplexer, having two inputs coupled to an output of the limiter and an output of the phase-locked loop respectively.
 4. The short-distance contactless communication apparatus of claim 1, further comprising: an adjusting device, coupled to the receiver, for adjusting a peak voltage level of the received modulation signal to fall within a predetermined voltage range.
 5. A short-distance contactless communication apparatus, comprising: a first receiver, coupled to a signal receiving port of the short-distance contactless communication apparatus, capable of operating under a proximity coupling device (PCD) mode and/or a proximity inductively coupled card (PICC) mode; and an adjusting device, coupled to the signal receiving port, for adjusting a peak voltage level of a modulation signal on the signal receiving port to fall within a predetermined voltage range.
 6. The short-distance contactless communication apparatus of claim 5, wherein the adjusting device presently adjusts the peak voltage level of the modulation signal on the signal receiving port when the short-distance contactless communication apparatus receives the modulation signal via the signal receiving port.
 7. The short-distance contactless communication apparatus of claim 5, wherein the adjusting device adjusts the peak voltage level of the modulation signal on the signal receiving port to substantially equal a predetermined voltage level in the predetermined voltage range.
 8. The short-distance contactless communication apparatus of claim 5, wherein the adjusting device adjusts the peak voltage level of the modulation signal on the signal receiving port to fall within the predetermined voltage range during the PCD mode of the short-distance contactless communication apparatus, and the modulation signal is an in-band blocker signal or a load modulation signal.
 9. The short-distance contactless communication apparatus of claim 5, which is an integrated NFC (Near field communication) device.
 10. The short-distance contactless communication apparatus of claim 5, wherein the modulation signal is anASK (Amplitude-shift keying) signal or a continuous wave (CW) signal having an oscillating frequency substantially equal to 13.56 MHz.
 11. The short-distance contactless communication apparatus of claim 5, further comprising: a second receiver, coupled to the signal receiving port, capable of operating under a PCD mode or a PICC mode.
 12. The short-distance contactless communication apparatus of claim 5, wherein the adjusting device adjusts the peak voltage level of the modulation signal on the signal receiving port to fall within the predetermined voltage range during the PICC mode of the short-distance contactless communication apparatus, and the modulation signal is a receiving ASK (Amplitude-shift keying) signal of the short-distance contactless communication apparatus.
 13. The short-distance contactless communication apparatus of claim 5, furthering comprising: a baseband processor, coupled to the receiver and the adjusting device; and wherein the adjusting device comprises: a programmable impedance component, having a first terminal coupled to the signal receiving port and a second terminal coupled to a reference voltage, for providing an impedance between the signal receiving port and the reference voltage according to an adjusting signal; and an envelope detector, coupled to the signal receiving port and the baseband processor, for detecting an envelope of the modulation signal to generate a detecting signal; wherein the baseband processor receives the detecting signal and accordingly generates the adjusting signal to adjust the impedance of the programmable impedance component such that the peak voltage level of the modulation signal on the signal receiving port falls within the predetermined voltage range.
 14. The short-distance contactless communication apparatus of claim 13, wherein the baseband processor adjusts the impedance of the programmable impedance component such that the peak voltage level of the modulation signal on the signal receiving port substantially equals a predetermined voltage level in the predetermined voltage range.
 15. A short-distance contactless communication method, comprising: using a first receiver capable of operating under a proximity coupling device (PCD) mode and/or a proximity inductively coupled card (PICC) mode to couple to a signal receiving port; and adjusting a peak voltage level of a modulation signal on the signal receiving port to fall within a predetermined voltage range.
 16. The short-distance contactless communication method of claim 15, wherein the step of adjusting the peak voltage level of the modulation signal on the signal receiving port to fall within the predetermined voltage range comprises: presently adjusting the peak voltage level of the modulation signal on the signal receiving port when the modulation signal appears on the signal receiving port.
 17. The short-distance contactless communication method of claim 15, wherein the step of adjusting the peak voltage level of the modulation signal on the signal receiving port to fall within the predetermined voltage range comprises: adjusting the peak voltage level of the modulation signal on the signal receiving port to substantially equal a predetermined voltage level in the predetermined voltage range.
 18. The short-distance contactless communication method of claim 15, wherein the step of adjusting the peak voltage level of the modulation signal on the signal receiving port to fall within the predetermined voltage range comprises: adjusting the peak voltage level of the modulation signal on the signal receiving port to fall within the predetermined voltage range during the PCD mode, and the modulation signal is an in-band blocker signal or a load modulation signal.
 19. The short-distance contactless communication method of claim 15, wherein the modulation signal is an ASK (Amplitude-shift keying) signal or a continuous wave (CW) signal having an oscillating frequency substantially equal to 13.56 MHz.
 20. The short-distance contactless communication method of claim 15, wherein the step of adjusting the peak voltage level of the modulation signal on the signal receiving port to fall within the predetermined voltage range comprises: adjusting the peak voltage level of the modulation signal on the signal receiving port to fall within the predetermined voltage range during the PICC mode, and the modulation signal is a receiving ASK (Amplitude-shift keying) signal.
 21. The short-distance contactless communication method of claim 15, wherein the step of adjusting the peak voltage level of the modulation signal on the signal receiving port to fall within the predetermined voltage range comprises: using a programmable impedance component having a first terminal coupled to the signal receiving port and a second terminal coupled to a reference voltage for providing an impedance between the signal receiving port and the reference voltage according to an adjusting signal; detecting an envelope of the modulation signal to generate a detecting signal; and receiving the detecting signal and accordingly generating the adjusting signal to adjust the impedance of the programmable impedance component such that the peak voltage level of the modulation signal on the signal receiving port falls within the predetermined voltage range.
 22. The short-distance contactless communication method of claim 21, wherein the step of receiving the detecting signal and accordingly generating the adjusting signal to adjust the impedance of the programmable resistor comprises: adjusting the impedance of the programmable impedance component such that the peak voltage level of the modulation signal on the signal receiving port substantially equals a predetermined voltage level in the predetermined voltage range.
 23. A NFC device comprising an NFC integrated circuit (IC) capable of supporting PCD and PICC reception, comprising: PCD and PICC receivers have a common input port; a fixed resistor coupled to the common input port; an envelope detector coupled to the common input port; a programmable resistor circuit having a first node coupled to the common input port and a second node coupled to ground; wherein the resistance of the programmable resistor circuit is adjusted according to the peak voltage level at the input of the envelope detector, and the adjustment of the programmable resistor circuit continues until the peak voltage at the input of the envelope detector is within a predetermined voltage range.
 24. The NFC device of claim 23, wherein the fixed resistor is placed within the NFC integrated circuit.
 25. The NFC device of claim 23, wherein during the PCD mode, the adjustment of the programmable resistor circuit is done at least once.
 26. The NFC device of claim 23, wherein during the PICC mode, the adjustment of the programmable resistor circuit is done at least once.
 27. The NFC device of claim 23, wherein the PCD and PICC receivers are integrated as a single receiver. 